And the running joke through the course was "If all other models fail, use simulation". Of course simulation was much more than the stop gap for problems where there was no neat technique. We learnt that operational research was useful for all kinds of problems, and especially the "Messy" ones. Lancaster's Skein House, where the O.R. Department was housed for many years, took its name form the two meanings of "skein". One, for untangling a skein of wool, and making sense of the messiness of it; two, for describing a group of geese, with humorous reference to O.R. sometimes being a "wild goose chase".
Simulation models over the years have been extremely useful, and the development of visual simulation models has been a boon to many O.R. workers who can demonstrate the "What happens if?" situation in their commercial situation. And the client can interact with what he/she can see. There are times when the best tool for the decision-maker is a pair of eyes, looking at the details of the model and using their brain while spotting how the system behaves.
Over the years, there have been many times when aspects of the work that I have done have highlighted the importance of eyes and brain. The client looks at how parts of the system perform and comments on those parts - as well as the primary objectives of the model. A well-constructed model needs to be geared to the brain of the client.
The other day, I was in correspondence about another area of commerce where mathematical modelling is not the complete answer to a business problem, although it has been used routinely for many problems.
|An irregular item, shrink-wrapped. The wrapping extends to the tapered neck, but it is noteworthy that there is no printing on the material which has shrunk there.|
Plastic shrink wrap is widely used in industry. Shrink material is a material that on a molecular level is a mass of twisted elastic bands. In the unheated material, these "bands" have been stretched till they are all tight and then they have been locked in that position. When heated they spring back to their happy knotted state and the film shrinks to its reduced size. The more that the material has to be shrunk, the more expensive it is. For some packaging all that is needed is to wrap a sheet around an object and then use a heat source to shrink the plastic. But there are many products on the shelves of shops and supermarkets where the shrink wrap carries the label. Just look at batteries, plastic bottles of juice, and cans of drinks. The label has been printed onto the material before it is shrunk, so the printing shrinks as well. So, the client knows what the final product should look like, and the printer has to work from that back to what should be printed, and where.
So far so good. If the object to be wrapped is a box, or a simple cylinder, then the printing will be straightforward, expanded in one or two dimensions. But, businesses want to wrap more complex shapes, such as cones, or the flattened cone shape used in spray cleaners.
So, the engineers work by a sort of adaptive process, starting with a printed grid being shrunk and then measured. Working back from the result, one can work out what to print and where. Just like a neat mathematical technique in O.R.
Unfortunately, this client had a circular logo which had to appear on the package. The engineers made their grids, measured them, and devised a print scheme with a distorted logo which would distort to appear correct when it was shrunk. It didn't work. Put bluntly, it looked wrong. The human eye could see that it wasn't quite a circle, and did not interpret it correctly.
So, here was a case for a sort of interactive simulation process of "What's best?" The engineers printed the logo in various places on the label, each design calculated to distort to the right shape. Then they worked alongside the client to see where his human eyes and brain interpreted the result as the company's circular logo. Where mathematics failed, the human eye and human brains won.
It was a good job that the engineers didn't rely on their models - they worked with the client to reach a "better" solution. Just as we in O.R. need to remember that the client knows best.